To help the SI units apply
to a wide range of phenomena, the 19th General
Conference on Weights and Measures in 1991
extended the list of metric prefixes so
that it reaches from yotta- at 1024 (one
septillion) to yocto- at 10-24 (one septillionth).
Here are the metric prefixes, with their
numerical equivalents stated in the American
system for naming large numbers:

SI
Unit Prefixes

Prefix

Symbol

Meaning

Base
Unit Multiplied by

Factor

yotta-

Y

septillion

1,000,000,000,000,000,000,000,000

1024

zetta-

Z

sextillion

1,000,000,000,000,000,000,000

1021

exa-

E

quintillion

1,000,000,000,000,000,000

1018

peta-

p

quadrillion

1,000,000,000,000,000

1015

tera-

T

trillion

1,000,000,000,000

1012

giga-

g

billion

1,000,000,000

109

mega-

M

million

1,000,000

106

kilo-

k

thousand

1,000

103

hecto-

h

hundred

100

102

deca-

da

ten

10

101

Base
units, no prefix - Ex.- meter,
liter, gram

100

deci-

d

tenth

0.1

10-1

centi-

c

hundredth

0.01

10-2

milli-

m

thousandth

0.001

10-3

micro-

u

millionth

0.000001

10-6

nano-

n

billionth

0.000000001

10-9

pico-

p

trillionth

0.000000000001

10-12

femto-

f

quadrillionth

0.000000000000001

10-15

atto-

a

quintillionth

0.000000000000000001

10-18

zepto-

z

sextillionth

0.000000000000000000001

10-21

yocto-

y

septillionth

0.000000000000000000000001

10-24

What's
it all mean?
A kilometer is a thousand meters, a kiloliter
is a thousand liters, a kilogram is a thousand
grams; a centimeter is a hundredth of a
meter, a centiliter is a hundredth of a
liter, a centigram is a hundredth of a gram.
The prefixes can be applied to any kind
of SI unit. Only temperature degrees (Celsius
or Kelvin in SI) seem to be exempt. Also,
there is no accepted metric time system
in use.